4.7.5 NAS signalling using trusted WLAN access network

A trusted WLAN interworking function (TWIF) provides functionalities for a non-5G capable over WLAN (N5CW) device to access 5GCN, including:

• NAS signalling over N1 NAS signalling connection with AMF; and
• PDU session establishment, modification and release on behalf of the N5CW device, over N2 connection with the AMF.

The TWIF registers on behalf of the N5CW device to an AMF according to clause 5.5.1 by populating the parameters for the registration by using implementation specific default values which are the same for N5CW devices.

The TWIF may request to establish a PDU session as specified in clause 6.4.1.2 on behalf of the N5CW device upon receipt of an IP configuration request from the N5CW device by populating either all the required parameters or part of the required parameters for the PDU session establishment by using implementation specific default values from the TWIF's configuration. Only one PDU session is supported when N5CW device accessing 5GCN via the TWIF.

NOTE 1: If part of the required parameters for the PDU session establishment is provided by the TWIF, the remaining of the required parameters are determined by the AMF or the SMF based on the N5CW device's subscription information.

Upon loss of the IP address of the N5CW device, the TWIF acting on behalf of the N5CW device shall initiate the UE-requested PDU session release procedure as defined in clause 6.4.3.

NOTE 2: The established PDU session on behalf of the N5CW device can be modified by the TWIF or the network.